This invention relates to guidewires for intravascular catheters.
There is a demand for increasingly smaller diameter guidewires to enable access to the distal reaches of the vascular system, particularly, the neurovascular system. Micro guidewires are those having a distal diameter of 0.010 inches or less. Such guidewires are capable in guiding catheters through much of the vascular system. However, there are limitations to the usefulness of micro guidewires.
One limitation relates to controllability of micro guidewires. Guidewires are typically rotated by twisting the proximal end to steer the distal end through the vasculature. Some of these guidewires have a tip at the distal end with a xe2x80x9cJxe2x80x9d shape. Rotation of the proximal end of the micro guide wire directs the distal tip to help steer the guidewire through the vasculature.
A micro guidewire having a small diameter will typically have a reduced torsional stiffness compared with guidewires of larger diameter. Rotation of the proximal end of the micro guide wire may not result in rotation of the distal tip when the micro guidewire is in use in a highly tortuous vessel, thus, reducing the ability to steer the distal tip of the micro guidewire to a desired target.
U.S. Pat. No. 5,313,967 to Lieber et al. discloses a guidewire having a helical length for transmitting torque and axial force. The distal tip tapers from the helix and is brazed to the tip spring. While the helical shape of the guidewire is beneficial, the Lieber et al fail to teach how improved torque and axial force transmission can be accomplished in the region of the distal tip.
U.S. Pat. No. 4,846,174 to Willard et al. discloses a guidewire having a flattened distal tip with a uniformly rectangular cross section. The spring has two ends. Each end of the spring attaches to the distal tip.
What is desired is a guidewire having a diameter small enough to access the distal reaches of the vasculature, including the neurovascualture and having sufficient torsional stiffness to enable steering of the guidewire through these tortuous regions. What is also desired is a micro guidewire having a distal end with improved tensile and torsional integrity, yet with the capability to readily bend in any direction.
A micro guidewire includes a core and a coil in composite cooperation. The core has a proximal region having a minimum outside diameter of 0.012xe2x80x3. The distal region includes a flattened end for connecting the core to the coil.
The coil winds about the distal region and has a maximum outside diameter of 0.0085xe2x80x3, a proximal end, a distal end and a length extending between the proximal end and the distal end.
Three joints attach the coil to the core. A distal joint attaches the distal end of the coil to the tip of the flattened end. A proximal joint attaches the proximal end of the coil to the core. A medial joint attaches the intermediate portion, i.e. length of the coil to the core. These three joints cooperate to provide improved tensile and torsional integrity to the distal region of the core. Accordingly, the coil and the core form a composite structure.
A discrete portion of the distal region is flattened to form a tang to optimize the torque carrying ability of the distal region. The medial joint forms at the tang, circumscribing the tang to improve the torsional integrity of the distal region of the core. The tang enhances lateral flexibility of the core as compared with a cylindrical section of the same nominal diameter. Furthermore, the tang improves the torsional responsiveness of the distal region. Preferably the tang has a uniform thickness. enabling composite cooperation between the coil and the core near the distal end of the coil. Preferably, the medial joint attaches no more than {fraction (1/3)} of the length away from the distal end.
According to one aspect of the invention, the preferable ratio of the diameter of the proximal end of the core to the outside diameter of the coil is at least 1.4 to 1. Having a relatively thick proximal end of the core improves the torsional efficience of the guidewire. In accordance with the present invention, the torsional efficiency achieved is around 80%, or better when the guidewire is in use within a tortuous vessel.